In the case of conventional semiconductor devices with a wiring substrate, external contacts are arranged on the underside of the wiring substrate and at least one semiconductor chip, e.g., a memory device such as a DRAM, is arranged on the upper side of the wiring substrate, in the center of the upper side of the wiring substrate.
If a conventional device of this type is to be used as a stackable semiconductor device for a semiconductor module comprising stacked semiconductor devices, only the edge regions of the wiring substrate can be available for the attachment of external contacts of a stacked semiconductor device, since the center of the upper side of the wiring substrate is taken up by the semiconductor chip. The number and arrangement of external contacts of the semiconductor device to be stacked is therefore very restricted, such that many known types of packages, such as BGA (Ball Grid Array) or LGA (Land Grid Array) packages, cannot be stacked on a conventional semiconductor device with a wiring substrate.
Solutions to this stacking problem are known in the art. For stacking, conventional semiconductor devices with a BGA or LGA package are provided with additional flexible wiring films that have a larger surface area than the semiconductor devices to be stacked and protrude beyond the edge of the semiconductor devices, such that the flexible wiring films can be bent in the direction of a semiconductor device of a semiconductor device stack that is arranged underneath and can be electrically connected to the semiconductor device arranged underneath via the flexible film.
A semiconductor module with semiconductor devices stacked in such a manner has the disadvantage that the semiconductor devices cannot be stacked with the lowest possible space requirement, especially since the bent wiring film requires a large enough bending radius to avoid the risk of microcracks in the wiring lines arranged on the wiring film.
In addition, such a semiconductor module has the disadvantage that the thickness of each stage of the stack includes the thickness of the semiconductor chip and the considerable thickness of the wiring substrate.